A free electron laser diagrammatically includes an electron source and an accelerating structure so as to provide these electrons with relativist speeds and diverse deflectors making it possible to introduce the accelerated beam into a magnetic structure known as a wiggler. This wiggler is formed of varying magnets creating a transverse magnetic field, varying or periodic. The beam of electrons inside this wiggler undergoes deflections inside the plane perpendicular to the magnetic field. At the outlet, the beam of electrons is again deflected by a deflector and finally absorbed by an attenuator. Two mirrors may frame the wiggler.
The wiggler is the seat of an interaction between the beam of electrons and an electromagnetic wave created during deflections of the beam. If certain conditions are observed, the electromagnetic wave is amplified at the expense of the energy of the beam of electrons. An intense coherent electromagnetic field is then emitted by the structure.
A description of this device appears in the U.S. Pat. No. 3,822,410 granted to John M. J. MADEY.
Free electron lasers are remarkable radiation sources for two reasons in particular: firstly as they allow for wavelength tuning and secondly, as the amplificator medium is constituted by a beam of electrons in a vacuum, they are able to function at extremely high power without being the center of breakdown phenomena encountered in other types of lasers (solid, gas or liquid lasers).
However, these devices in certain applications do have one drawback. The spectrum of the radiation they emit is extremely wide and generally evolves chaotically from one passage to another in the wiggler. In any event, the width of the spectrum is determined by the manufacturer and in certain cases, it would be desired to be able to adjust this width so as to optimize it according to the application.
So as to obtain this result, it is possible to introduce into the interaction zone various wavelength selection means which are functionally equivalent to a monochromator. However, having done this, one of the advantages mentioned above would disappear, namely the absence of any equipment medium capable of impeding obtaining extremely high powers.